1. Field of the Invention
The present invention relates to the manufacture of porous ceramic particulate filters, and more particularly to improved materials and processes for sealing selected channels of porous ceramic honeycombs to form wall-flow ceramic filters therefrom.
2. Technical Background
Ceramic wall flow filters are finding widening use for the removal of particulate pollutants from diesel or other combustion engine exhaust streams. A number of different approaches for manufacturing such filters from channeled honeycomb structures formed of porous ceramics are known. The most widespread approach is to position cured plugs of sealing material at the ends of alternate channels of such structures which can block direct fluid flow through the channels and force the fluid stream through the porous channel walls of the honeycombs before exiting the filter. Illustrative of this approach is U.S. Pat. No. 6,809,139, which describes the use of sealing materials comprising cordierite-forming (MgO—Al2O3—SiO2) ceramic powder blends and thermosetting or thermoplastic binder systems to form such plugs.
For most of their manufacturing history, Diesel Particulate Filters have been comprised of cordierite (magnesium alumino silicate) as the base ceramic material. However, cordierite has potential short comings when uncontrolled regeneration of the filter occurs during normal operation. Namely, the material typically melts at about 1435° C. and it has a relatively low heat capacity. In extreme cases this can cause melting of the filter matrix, and failure of the filter. To this end, aluminum titanate has been proposed as a viable alternate ceramic material for forming ceramic wall flow filters due to its higher melt temperature and relatively high heat capacity compared to cordierite. However, because aluminum titanate material is generally incompatible with cordierite, there is a need in the art for a plugging material that is compatible with aluminum titanate.